Since propylene polymers and propylene/α-olefin copolymers are not only inexpensive but also excellent in mechanical physical properties, heat resistance, chemical resistance, water resistance, etc., they are used over wide fields. However, since such propylene-based polymers do not have a polar group in the molecule thereof, they are generally low in polarity and involve a drawback that painting or adhesion is difficult. For the purpose of remedying this drawback, there have been attempted various measures such as chemical treatment of the surface of a molded article of the subject propylene polymer with a chemical and oxidation treatment of the surface of the molded article by means of corona discharge treatment, plasma treatment, flame treatment, etc. Nevertheless, according to these methods, not only special units are required, but also it cannot be said that an improving effect of painting properties or adhesion properties is satisfactory.
Then, as a device for imparting good painting properties or adhesion properties to propylene-based polymers by a relatively simple method, there have been developed so-called chlorinated polypropylene and acid-modified propylene/α-olefin copolymers. In general, since isotactic polypropylene is insoluble in solvents, there has been made a device in which the isotactic polypropylene is chlorinated, or propylene is copolymerized with an α-olefin to lower crystallinity, thereby revealing solubility. Also, since the crystallinity is reduced by applying acid modification, resins having relatively good solubility due to the acid modification were obtained. However, there was encountered a problem that following an increase of the modification amount, adhesion properties with a polypropylene-based resin is inferior so that solubility and adhesion are contrary to each other. Also, in addition to this problem, there was encountered a problem that when such a resin is used in a paint, etc., compatibility with polar resins is low so that the resin cannot be mixed with an acrylic resin, etc.
In JP-A-3-229772, a resin obtained by graft co-polymerizing a reactive unsaturated compound having at least one of a hydroxyl group, a glycidyl group, and an amino group on an acid-modified propylene/α-olefin copolymer is shown as a resin having improved compatibility, and a coating composition for polyolefin-based resin containing this resin is also disclosed. However, while this composition is improved with respect to the solubility and compatibility by applying modification such as copolymerization with an α-olefin copolymer, acid modification, and grafting of a polar resin to the resin to be contained therein, there is pointed out a problem that it is inferior in adhesion.